Offset compensation for serial links

ABSTRACT

A method for compensating an offset in a receiver is provided. The method includes receiving first data from a first sampler and receiving second data from a second sampler. The method also include determining a first average value from the boundary of the first data over a selected period of time; and sending an offset signal to the first sampler based on the first average value. The method may also include determining a second average value from the boundary of the second data over a selected period of time; and sending an offset signal to the second sampler based on the second average value of the boundary data.

FIELD

The embodiments discussed herein are related to offset compensation forserial links.

BACKGROUND

Serial receivers employ amplifiers and/or samplers whose input signalsswing for a number of reasons. These offsets may be a function ofenvironment, age, use, etc., and may vary slowly over time. Theseoffsets may degrade receiver performance and in the extreme may saturatethe output and possibly lead to receiver failure.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one example technology area where some embodiments describedherein may be practiced.

SUMMARY

According to an aspect of an embodiment, a method for compensating anoffset in a receiver is provided. The method includes receiving firstdata from a first sampler and receiving second data from a secondsampler. The method also include determining a first average value fromthe boundary of the first data over a selected period of time; andsending an offset signal to the first sampler based on the first averagevalue. The method may also include determining a second average valuefrom the boundary of the second data over a selected period of time; andsending an offset signal to the second sampler based on the secondaverage value of the boundary data.

The object and advantages of the embodiments will be realized andachieved at least by the elements, features, and combinationsparticularly pointed out in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a block diagram of an example serial receiver according to atleast one embodiment described herein.

FIG. 2A illustrates an example timing diagram of a differential signalaccording to at least one embodiment described herein.

FIG. 2B illustrates an example timing diagram of a data clock accordingto at least one embodiment described herein.

FIG. 2C illustrates an example timing diagram of a boundary clockaccording to at least one embodiment described herein.

FIG. 2D illustrates an example timing diagram of an edge signalaccording to at least one embodiment described herein.

FIG. 3 is a block diagram of an example serial receiver according to atleast one embodiment described herein.

FIG. 4 is a flowchart of an example online process for correcting offsetof a sampler according to at least one embodiment described herein.

FIG. 5 is another flowchart of an example online process for correctingoffset of a sampler according to at least one embodiment describedherein.

FIG. 6 is a flowchart of an example process for correcting offsets usingfour samplers according to some embodiments described herein.

FIG. 7 is another flowchart of an example online process for correctingoffset of a sampler according to at least one embodiment describedherein.

FIG. 8A illustrates an example timing diagram of a differential signalaccording to at least one embodiment described herein.

FIGS. 8B, 8C, 8D and 8E illustrate different clocks that are ninetydegrees out of phase relative to neighboring clocks according to atleast one embodiment described herein.

DESCRIPTION OF EMBODIMENTS

Serial communication receivers may employ a number of amplifiers and/orsamplers whose input offset may be on the order of tens of millivoltsfor a number of reasons. This offset may be a function of processvariation, environment, age, use, etc., and may vary slowly over time.These offsets may degrade receiver performance and in the extreme maysaturate the output and possibly lead to receiver failure.

Offset compensation techniques and/or receivers that provide onlineoffset compensation are disclosed in accordance with at least oneembodiment described herein. These techniques and/or receivers maycompensate for voltage offsets in amplifiers and/or samplers (or anyother component) in a serial link without requiring additional samplersor amplifiers. Moreover, in accordance with at least one embodimentdescribed herein, offset compensation may occur online. For example,offset compensation may occur while data samples are collected from aninput signal. According to some embodiments described herein, thesetechniques and/or receivers may include a data sampler that generatesdata samples and a boundary sampler that generates boundary samples.These techniques and/or receivers may use information from the boundarysamples to extract an offset of the boundary sampler and provide offsetcompensation of the amplifiers and/or samplers (or other components)using the extracted offset. After extracting the offset, the role of thedata samplers and boundary samplers may be switched and the offset ofthe new boundary sampler may be extracted and applied.

Embodiments of the present invention will be explained with reference tothe accompanying drawings.

FIG. 1 is a block diagram of an example receiver system 100 according toat least one embodiment described herein. The receiver system 100 mayinclude any type of receiver such as, for example, an electricalwireline receiver, an optical receiver, a Wi-Fi receiver, a Bluetoothreceiver, an LTE receiver, or any other digital communication receivers,such as receivers on printed circuit boards, integrated circuits, andother receivers.

The receiver system 100 may include an amplifier 105, a first sampler110, a second sampler 115, a clock and data recovery circuit and/orphase detector (CDR-PD) 120, and a clock generator 125. The amplifier105 may include any number of amplifiers. Similarly, any number ofsamplers may be used including the first sampler 110 and the secondsampler 115.

The amplifier 105 may be configured to receive a signal, such as adifferential signal. The amplifier 105 may amplify the differentialsignal and provide the differential signal to the first sampler 110 andthe second sampler 115. FIG. 2A illustrates an example timing diagram ofa differential signal, according to at least one embodiment describedherein. The differential signal may include a first signal, do, andsecond signal, dox, respectively, that may vary between two voltages,V_(S) and V₀. For example, V₀ may be zero volts and V_(S) may be near orless than 1 volt. As another example, V_(S) may be 500 mV and V₀ may be−500 mV. Other voltage levels may be used as well. The first signal andthe second signal (do and dox) may be complements of one another: onesignal may be asserted while the other is not and vice versa.

Returning to FIG. 1, the first sampler 110 and/or the second sampler 115may include a number of different components and/or circuits. The firstsampler 110 and/or the second sampler 115 may include, for example, acomparator that compares a voltage of the first signal and second signalof the differential signal at the rising edge and/or falling edge of aclock provided to each of the first sampler 110 and the second sampler115. In some embodiments, the first sampler 110 may be configured toreceive a first clock from the clock generator 125, and the secondsampler 115 may be configured to receive a second clock from the clockgenerator 125. In some embodiments, the first clock and the second clockmay have the same frequency but a different phase. Alternately oradditionally, the first clock and the second clock may have a similarfrequency and phase. For example, the first clock may be out of phasewith the second clock by 90, 180, or 270 degrees, or by some otheramount.

Based on the comparison of the voltage of first signal to the voltage ofthe second signal, the first sampler 110 and the second sampler 115 maysend digital data representing the comparison to the CDR-PD 120. Forexample, when the comparison between the voltages of first signal to thevoltage of the second signal indicates that the voltage of the firstsignal is larger than the voltage of the second signal, the firstsampler 110 and/or the second sampler 115 may output digital datarepresenting a digital one (e.g., an asserted bit). Alternately, whenthe comparison between the voltages of first signal to the voltage ofthe second signal indicates that the voltage of the first signal issmaller than the voltage of the second signal, the first sampler 110and/or the second sampler 115 may output digital data representing adigital zero (an unasserted bit).

In some embodiments, when the first clock and the second clock have thesame frequency but a different phase, one of the first clock and thesecond clock may cause one of the first sampler 110 and the secondsampler 115 to sample the differential signal when the first signal andthe second signal of the differential signal are transitioning and atother times. The clock signal of the first clock and/or the second clockthat may cause one of the first sampler 110 and the second sampler 115to sample the differential signal when the first and second signals ofthe differential signal are transitioning may be referred to as aboundary clock. The first and second signals may be transitioning, whenthe first signal is changing from being V_(S) to V₀ and the secondsignal is changing from being V₀ to V_(S), and/or vice-versa. Thedigital data sampled using the boundary clock may be referred to asboundary data. The one of the first sampler 110 and the second sampler115 that samples using the boundary clock may be referred to herein asthe boundary sampler.

The other of the first clock and the second clock may cause one of thefirst sampler 110 and the second sampler 115 to sample the differentialsignal approximately half-way between transitions of the first andsecond signals of the differential signal. The clock signal of the firstclock and/or the second clock that may cause one of the first sampler110 and the second sampler 115 to sample the differential signalapproximately half-way between transitions of the first and secondsignals of the differential signal may be referred to as a data clock.The digital data sampled using the data clock may be referred to as thedata of the differential signal or simply data The one of the firstsampler 110 and the second sampler 115 that samples using the data clockmay be referred to herein as the data sampler.

FIG. 2B illustrates an example timing diagram of a data clock and FIG.2C illustrates an example timing diagram of a boundary clock, accordingto at least one embodiment described herein. As illustrated byreferencing FIGS. 2A and 2B, the rise of the data clock occurs in themiddle of a data bit of the differential signal illustrated in FIG. 2A.As illustrated by referencing FIGS. 2A and 2C, some rises of theboundary clock occurs at the boundary of the differential signalillustrated in FIG. 2A. As noted above, one of the first sampler 110 andthe second sampler 115 may be selected as the boundary sampler and maybe clocked using the boundary clock illustrated in the timing diagram ofFIG. 2C. The other sampler may be used to sample the data and may beclocked using the data clock illustrated in the timing diagram of FIG.2B.

Returning to FIG. 1, the first sampler 110, the second sampler 115,and/or the amplifier 105 may be subject to voltage offsets. For example,the first sampler 110 may include a comparator that compares a voltageof the first signal of the differential signal to a voltage of thesecond signal of the differential signal. When the first sampler 110 hasno offset, the first sampler 110 may output a digital one when sampledafter the voltage levels of the first and second signal cross asillustrated in FIG. 2A. When the first sampler 110 has an offset, forexample, an offset of 100 millivolts (mV), the first sampler 110 mayoutput a digital one when sampled after the voltage of the first signalplus 100 mV exceeds the voltage of the second signal. These offsets mayvary over time and may be as much as, for example, ±5 mV, ±10 mV ±50 mV,±100 mV, etc.

Offsets in the boundary sampler may result in the boundary data beingdifferent then if the boundary sampler did not have an offset. Forexample, when the first sampler 110 is the boundary sampler and has noor little offset, the first sampler 110 may sample the differentialsignal when the boundary clock (see FIG. 2C) rises. As a result, thefirst sampler 110 may sample the differential signal at the boundary,when the first and second signals are transitioning. In particular, thefirst sampler 110 may sample the differential signal when the first andsecond signals are approximately equal. Because of jitter, noise, phasemisalignment of the boundary clock and other variables, the firstsampler 110 may sometimes output digital zero or a digital one. Overtime, an average of the digital data outputs of the first sampler 110may approximately equal one-half (½). In some embodiments, the averageof the digital data outputs of the first sampler 110 may vary by plus orminus 5%, 10%, 15% or 20%. In contrast, when the first sampler 110 isthe boundary sampler and has a positive offset, the first sampler 110may sample at the boundary of the differential signal and may more oftenoutput a digital one than a digital zero because the voltage of thefirst signal plus the positive offset may be greater than the voltage ofthe second signal when the sampling occurs. As a result, an average ofthe digital data outputs of the first sampler 110 may not approximatelyequal one-half, but may be greater than one-half. Alternately, with anegative offset, the first sampler 110 sampling at the boundary of thedifferential signal may more often output a digital zero than a digitalone. As a result, an average of the digital data outputs of the firstsampler 110 may be less than one-half.

The CDR-PD 120 may include edge detection circuitry, phase-lock-loopcircuitry, linear phase detectors, binary phase detectors, rotationalphase detectors, quadricorrelators, etc. The CDR-PD 120 may beconfigured to input digital data sampled by the first sampler 110 andthe second sampler 115. In some embodiments, the digital data from oneof the two samplers may be boundary data and the other digital data maybe data. By detecting a phase difference between when the boundary datais received and the data is received, the CDR-PD 120 may determineinformation for adjusting the phase and/or frequency of the boundaryclock and the data clock provided to the first sampler 110 and thesecond sampler 115. In some embodiments, the CDR-PD 120 may also inputdata from any number of other samplers and may use at least one of thesampler's data as the boundary data.

The CDR-PD 120 may output a clock adjustment signal to the clockgenerator 125 that may indicate adjustments for the boundary clock andthe data clock so that the frequency and phase of the boundary clock maybe aligned with the differential signal and/or so that the frequency ofthe data clock is aligned with the differential signal, but the phase ofthe data clock may be offset from the phase of the differential signal.For example, the clock generator 125 may include a voltage-controlledoscillator and the CDR-PD 120 may output a voltage that may be used bythe voltage-controlled oscillator to synchronize the boundary clock tothe frequency and phase of the differential signal.

In some embodiments, the CDR-PD 120 may also output an edge signal asillustrated in FIG. 2D. The edge signal may or may not be used inembodiments described herein. The edge signal, for example, may indicatewhere the signal transitions form high values to low values or from lowvalues to high values. As illustrated in FIGS. 2A and 2D, the edgesignal is asserted when the signal in FIG. 2A transitions between highand low values. Embodiments described herein use boundary data sampledat these transitions to determine offset compensation for the amplifier105, the sampler 110, and/or the sampler 115.

In some embodiments, because the boundary data is sampled on theboundary clock, the boundary data includes some data that is sampledduring transitions and some data that is not sampled during transitions.For example, when the differential signal is asserted for multiplecontiguous clock cycles no transitions occur and the boundary dataincludes samples of the differential signal that is not part of atransition. The edge signal may be used to indicate the portions of theboundary data that represents transitions in the differential signal.These portions of the boundary data may be averaged over time and usedfor offset compensation.

FIG. 3 is a block diagram of an example receiver 300, according to atleast one embodiment described herein. The receiver 300 includes offsetlogic 130 coupled with the CDR-PD 120, the clock generator 125, thefirst sampler 110, and the second sampler 115. The offset logic 130 mayreceive boundary data from the CDR-PD 120 and may determine an offset byaveraging the boundary data.

The offset logic 130 may also include logic that indicates to the CDR-PD120 which data of the data from the first sampler 110 and/or the secondsampler 115 (or any other samplers) to use as the boundary data.Additionally or alternatively, the offset logic 130 may also send asignal to the clock generator 125 specifying whether to send the dataclock or the boundary clock to the first sampler 110 or the secondsampler 115 (or any other samplers). The offset logic 130 may includememory, logic, and/or a controller. Moreover, the CDR-PD 120 and theoffset logic 130, for example, may be part of the same component orcircuitry.

The offset logic 130 alone or in conjunction with other components(e.g., the other components of receiver 400) may also perform all orportions of process 400 illustrated in FIG. 4, process 500 illustratedin FIG. 5, process 600 illustrated in FIG. 6, or process 700 illustratedin FIG. 7.

FIG. 4 is a flowchart of an example process 400 for correcting offset ofa sampler, according to at least one embodiment described herein. Atblock 405, the data sampled by the first sampler 110 may be used for thedata and the data sampled by the second sampler 115 may be used for theboundary data. For example, the offset logic 130 may send a signal tothe CDR-PD 120 that indicates that the data sampled by the first sampler110 may be set as data and the data sampled by the second sampler 115may be set as the boundary data. The CDR-PD 120 may send the boundarydata to the offset logic 130.

Since the data sampled by the second sampler 115 is the boundary data,the clock generator 125 may send the boundary clock (e.g., FIG. 2C) tothe second sampler 115 and the data clock (e.g., the data clockillustrated in FIG. 2B) to the first sampler 110. For example, theoffset logic 130 may send a signal to the clock generator 125 indicatingwhich sampler to send the data clock and which sampler to send theboundary clock.

At block 410, the offset logic 130 may average the boundary data over aselected period of time. The boundary data, for example, may be averagedover a selected period of time or a selected number of clock cycles.

At block 415 the offset of the second sampler 115 may be compensatedbased on whether the average value of the boundary data is greater thanor less than one-half. For example, if the offset logic 130 determinesthat the average value of the boundary data is asserted is greater thanone-half, then the offset logic 130 may send a signal to the secondsampler 115 to adjust the sampler by a selected negative amount. Asanother example, if the offset logic 130 determines that the averagevalue of the boundary data is asserted is less than one-half, then theoffset logic 130 may send a signal to the second sampler 115 to adjustthe sampler by a selected positive amount. The selected negative amountand/or positive amount, for example, may be ±1 mV, ±5 mV, ±10 mV, ±50mV, ±100 mV, ±200 mV, etc. As yet another example, the offset logic 130may indicate an offset value to the second sampler 115 that isproportional to a difference between the average value of the boundarydata is asserted and one-half.

Alternatively or additionally, the offset of the first sampler 110 mayalso be compensated based on the comparison of the average value of theboundary data is asserted. For example, if the offset logic 130determines that the average value of the boundary data is asserted isgreater than one-half, then the offset logic 130 may send a signal tothe first sampler 110 to adjust the sampler by a selected negativeamount. As another example, if the offset logic 130 determines that theaverage value of the boundary data is asserted is less than one-half,then the offset logic 130 may send a signal to the first sampler 110 toadjust the sampler by a selected positive amount. The selected negativeamount and/or positive amount, for example, may be ±1 mV, ±5 mV, ±10 mV,±50 mV, ±100 mV, ±200 mV, etc. As another example, the offset logic 130may indicate an offset value to the first sampler 110 that isproportional to a difference between the average value of the boundarydata is asserted and one-half.

At block 420 the first sampler 110 and the second sampler 115 may beswapped. For example, the data sampled by the first sampler 110 may beused for the boundary data and the data sampled by the second sampler115 may be used as data. For example, the offset logic 130 may send asignal to the CDR-PD 120 that indicates that the data sampled by thesecond sampler 115 may be used for data and the data sampled by thefirst sampler 110 may be used for the boundary data. The CDR-PD 120 maythen send the data sampled by the first sampler 110 as the boundary datato the offset logic 130, and/or send the edge signal recovered from theboundary data to the offset logic 130.

At block 425 the boundary clock may be sent to the first sampler 110 andthe data clock may be sent to the second sampler 115. For example, theoffset logic 130 may send a signal to the clock generator 125 thatindicates the boundary clock may be sent to the first sampler 110 andthe data clock may be sent to the second sampler 115. Blocks 420 and 425may occur in any order and may occur simultaneously. As another example,the phases of the clocks sent to the respective samplers may be shiftedby ninety degrees.

According to at least one embodiment described herein, block 425 may beskipped. This block may be skipped, for example, if the clock generator125 does not support clock flipping. As another example, block 425 maybe skipped when the CDR-PD 120 has been locked to a specific clockfrequency. Alternatively, block 425 may be skipped for any other reason.

Alternatively or additionally, in some embodiments, after block 425, theoffset logic 130 and/or CDR-PD 120 may pause for a set period of time toallow any transient issues to settle that may occur when flipping theclocks. The time for the transient issues to settle may depend on thefrequency of the differential signal, jitter, and noise, among others.In one example, the receiver 300 may pause for 100 milliseconds.Alternatively or additionally, the receiver 300 may pause for a selectednumber of clock cycles.

Alternatively, in some embodiments, a pause for a set period of time maynot be needed following block 425. For instance, the clock phases may bechanged implemented in a single cycle in a synchronized and glitch-lessmanner. Each data bit, for example, may be captured by exactly one clockphase and/or no bits may be missed. This may result in no increase tothe bit error rate of the receiver. This is illustrated, for example, inFIGS. 8A, 8B, 8C, 8D and 8E. As illustrated in the figure, at time 805the phase of each clock is shifted by 90°. FIG. 8B shows a clock andFIG. 8C shows a boundary clock for the first sampler 110. FIG. 8D showsa clock and FIG. 8E shows a boundary clock for the second sampler 115.The shift can be made to transition a sampler from boundary mode to datamode.

At block 430, the offset logic 130 may average the boundary data over aselected period of time or a selected number of clock cycles.

At block 435 the offset of the first sampler 110 may be compensatedbased on whether the average value of the boundary data is asserted isgreater than or less than one-half. For example, if the offset logic 130determines that the average value of the boundary data is asserted isgreater than one-half, then the offset logic 130 may send a signal tothe first sampler 110 to adjust the sampler by a selected negativeamount. As another example, if the offset logic 130 determines that theaverage value of the boundary data is asserted is less than one-half,then the offset logic 130 may send a signal to the first sampler 110 toadjust the sampler by a selected positive amount. The selected negativeamount and/or positive amount, for example, may be ±1 mV, ±5 mV, ±10 mV,±50 mV, ±100 mV, ±200 mV, etc. As yet another example, the offset logic130 may indicate an offset value to the first sampler 110 that isproportional to a difference between the average value of the boundarydata is asserted and one-half.

Alternatively or additionally, the offset of the second sampler 115 mayalso be compensated based on the comparison of the average value of theboundary data is asserted. For example, if the offset logic 130determines that the average value of the boundary data is asserted isgreater than one-half, then the offset logic 130 may send a signal tothe second sampler 115 to adjust the sampler by a selected negativeamount. As another example, if the offset logic 130 determines that theaverage value of the boundary data is asserted is less than one-half,then the offset logic 130 may send a signal to the second sampler 115 toadjust the sampler by a selected positive amount. The selected negativeamount and/or positive amount, for example, may be ±1 mV, ±5 mV, ±10 mV,±50 mV, ±100 mV, ±200 mV, etc. As another example, the offset logic 130may indicate an offset value to the second sampler 115 that isproportional to a difference between the average value of the boundarydata is asserted and one-half.

After block 435, process 400 may return to block 405. Alternatively oradditionally, process 400 may be interrupted or stopped for any numberof reasons.

FIG. 5 is a flowchart of an example process 500 for correcting offset ofa sampler, according to at least one embodiment described herein.Process 500, for example, may be executed by receiver 300 illustrated inFIG. 3. Some of the blocks of process 500 may be similar to blocks ofprocess 400 illustrated in FIG. 4.

Process 500 may start at block 505, which may be similar to block 405illustrated in FIG. 4. At block 505, for example, the data sampled bythe first sampler 110 may be used for the data and the data sampled bythe second sampler 115 may be used for the boundary data.

Block 510 may be similar to block 410 illustrated in FIG. 4. At block510, the boundary data may be used to extract the offset for the secondsampler 115 as described herein. Block 515 may be similar to block 415illustrated in FIG. 4. At block 515 the offset of the second sampler 115may be corrected. For example, a signal may be sent to the secondsampler 115 indicating the magnitude and/or direction of the offset.

At block 520, the clock to the second sampler 115 may be adjusted sothat it is aligned to collect data rather than boundary data. Forinstance, the phase of the clock to the second sampler 115 may bealigned with the clock to the first sampler 110.

At block 525, data from both the first sampler 110 and the secondsampler 115 may be used as the data. For instance, after the offset ofthe second sampler 115 has been compensated, the process may enter adata collection state and data from both the first sampler 110 and thesecond sampler 115 may be used as data.

At block 530, the clock to the first sampler 110 may be adjusted so thatthe first sampler 110 samples the boundary. For instance, prior to block530, the first sampler 110 may use the clock in FIG. 2B, and may changeto the clock in FIG. 2C at block 530. In some embodiments, process 500may wait a predetermined or selected period of time prior to proceedingto block 530.

Block 535 may be similar to block 420 in FIG. 4. At block 535, the datasampled by the second sampler 115 may be used for the data and the datasampled by the first sampler 110 may be used for the boundary data.

Block 540 may be similar to block 430. At block 540, the boundary datacollected from the first sampler 110 may be used to extract the offsetof the sampler as discussed elsewhere herein. At block 545, the offsetof the first sampler 110 may be corrected. For example, a signal may besent to the first sampler 110 indicating the magnitude and/or directionof the offset.

At block 550, the clock to the first sampler 110 may be adjusted so thatit is aligned to collect data rather than boundary data. For instance,the phase of the clock to the first sampler 110 may be aligned with theclock to the second sampler 115.

At block 555, data from both the first sampler 110 and the secondsampler 115 may be used as the data. For instance, after the offset ofthe second sampler 115 has been compensated, the process may enter adata collection state and data from both the first sampler 110 and thesecond sampler 115 may be used as data.

At block 560, the clock to the second sampler 115 may be adjusted sothat the second sampler 115 samples the boundary. For instance, prior toblock 560, the second sampler 115 may use the clock in FIG. 2B, and maychange to the clock in FIG. 2C at block 530. In some embodiments,process 500 may wait a predetermined or selected period of time prior toproceeding to block 560.

Following block 530, process 500 may return to block 505. Process 500may end at any time. For example, process 500 may end after block 555 or560.

FIG. 6 is a flowchart of an example process 600 for correcting offsetsusing four samplers according to some embodiments described herein.While four samplers are described, process 600 may be expanded to anynumber of samplers or components. Process 600 starts at block 605.Sampler A1 and sampler A2 may be used to sample data from the signal andsampler B1 and sampler B2 may be used to sample the boundary of thesignal. These samplers may be selected and/or labeled in any order orconfiguration. Moreover, sampler A1 and sampler A2 may use the clockillustrated in FIG. 2B and sampler B1 and sampler B2 may use theboundary clock illustrated in FIG. 2C.

At block 610 the offsets for sampler B1 and sampler B2 may be determinedfrom the boundary of the signal according to various embodimentsdescribed herein and, at block 615; these offsets may be corrected insampler B1 and sampler B2.

At block 620 the clocks to sampler A1 and sampler B1 may be swapped. Forexample, sampler A1 may now use the boundary clock illustrated in FIG.2C and sampler B1 may use the clock illustrated in FIG. 2B.

At block 625, sampler B1 and sampler A2 may be used to sample data fromthe signal and sampler A1 and sampler B2 may be used to sample theboundary of the signal.

At block 630, the offset for sampler A1 may be corrected. The offset maybe determined from the boundary of the signal according to variousembodiments described herein.

At block 635 the clocks to sampler A2 and sampler B2 may be swapped. Forexample, sampler A2 may now use the boundary clock illustrated in FIG.2C and sampler B2 may use the clock illustrated in FIG. 2B.

At block 640, sampler B1 and sampler B2 may be used to sample data fromthe signal and sampler B1 and sampler B2 may be used to sample theboundary of the signal.

At block 645, the offset for sampler A2 may be corrected. The offset maybe determined from the boundary of the signal according to variousembodiments described herein.

At block 650 the clocks to sampler A1 and sampler B1 may be swapped. Forexample, sampler B1 may now use the boundary clock illustrated in FIG.2C and sampler A1 may use the clock illustrated in FIG. 2B.

At block 655, sampler A1 and sampler B2 may be used to sample data fromthe signal and sampler B1 and sampler A2 may be used to sample theboundary of the signal.

At block 660, the offset for sampler B1 may be corrected. The offset maybe determined from the boundary of the signal according to variousembodiments described herein.

At block 665 the clocks to sampler A2 and sampler B2 may be swapped. Forexample, sampler B2 may now use the boundary clock illustrated in FIG.2C and sampler A2 may use the clock illustrated in FIG. 2B.

At block 670, sampler A1 and sampler A2 may be used to sample data fromthe signal and sampler B1 and sampler B2 may be used to sample theboundary of the signal.

At block 675, the offset for sampler B2 may be corrected. The offset maybe determined from the boundary of the signal according to variousembodiments described herein.

Process 600 may then return to block 620. Process 600 may end at anytime.

FIG. 7 is a flowchart of an example process 700 for correcting offsets,according to at least one embodiment described herein. Process 700, forexample, may be executed at least in part by the receiver 300illustrated in FIG. 3. Process 700 begins at block 705, which may besimilar to block 405 in FIG. 4. At block 705, data sampled by the firstsampler 110 may be used for data and the data sampled by the secondsampler 115 may be used for the boundary data. At block 710, a CDR, forexample, within the CDR-PD 120 may be locked by extracting timing fromand locking the timing to the boundary data. The CDR may be locked usingany technique known in the art or used by a CDR.

Block 715 may be similar to block 410, block 720 may be similar to block415, and block 725 may be similar to block 420 all of process 400 inFIG. 4. At block 725, data sampled by the second sampler 115 may be usedfor data and the data sampled by the first sampler 110 may be used forthe boundary data.

At block 730, the CDR may be locked again using the first sampler 110data as the new boundary data. Block 735 may be similar to block 430 inFIG. 4 and block 740 may be similar to block 435 in FIG. 4. After block740, process 700 may return to block 705 where the process is repeated.

Alternatively or additionally, in any of processes illustrated in FIGS.5, 6, 7, and 8 the process may perform offset compensation for onesampler based on the rate of change of the offset of another sampler.For example, during offset compensation on the second sampler 115 aninitial offset may be noted for the second sampler 115. Then offsetcompensation may shift to the first sampler 110 and an initial offsetmay be noted for the first sampler 110. Offset compensation may occurfor a selected period of time (or indefinitely) for the first sampler110. It may be assumed that the second sampler 115 is subject to thesame environmental conditions as the first sampler 110. The offset ofthe second sampler 115, therefore, may be assumed to change over time ina manner similar to the first sampler 110. The offset compensation forthe second sampler 115 may be determined based on the rate of change ofthe first sampler 110 and the initial offset of the second sampler 115.

The embodiments described herein, in particular, the offset logic 130,may include the use of a special purpose or general purpose computerincluding various computer hardware or software modules, as discussed ingreater detail below.

Embodiments described herein may be implemented using computer-readablemedia for carrying or having computer-executable instructions or datastructures stored thereon. Such computer-readable media may be anyavailable media that may be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media may include tangible computer-readable storagemedia including Random Access Memory (RAM), Read-Only Memory (ROM),Electrically Erasable Programmable Read-Only Memory (EEPROM), CompactDisc Read-Only Memory (CD-ROM) or other optical disk storage, magneticdisk storage or other magnetic storage devices, flash memory devices(e.g., solid state memory devices), or any other storage medium whichmay be used to carry or store desired program code in the form ofcomputer-executable instructions or data structures and which may beaccessed by a general purpose or special purpose computer. Combinationsof the above may also be included within the scope of computer-readablemedia.

Computer-executable instructions may include, for example, instructionsand data which cause a general purpose computer, special purposecomputer, or special purpose processing device (e.g., one or moreprocessors) to perform a certain function or group of functions.Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

As used herein, the terms “module” or “component” may refer to specifichardware implementations configured to perform the operations of themodule or component and/or software objects or software routines thatmay be stored on and/or executed by general purpose hardware (e.g.,computer-readable media, processing devices, etc.) of the computingsystem. In some embodiments, the different components, modules, engines,and services described herein may be implemented as objects or processesthat execute on the computing system (e.g., as separate threads). Whilesome of the system and methods described herein are generally describedas being implemented in software (stored on and/or executed by generalpurpose hardware), specific hardware implementations or a combination ofsoftware and specific hardware implementations are also possible andcontemplated. In this description, a “computing entity” may be anycomputing system as previously defined herein, or any module orcombination of modulates running on a computing system.

All examples and conditional language recited herein are intended forpedagogical objects to aid the reader in understanding the invention andthe concepts contributed by the inventor to furthering the art, and areto be construed as being without limitation to such specifically recitedexamples and conditions. Although embodiments of the present inventionshave been described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A method for compensating an offset in areceiver, the method comprising: receiving first data from a firstsampler; receiving second data from a second sampler; determining afirst average value from a boundary of the first data over a firstselected period of time; sending an offset signal to the first samplerbased on the first average value; determining a second average valuefrom the boundary of the second data over a second selected period oftime; and sending an offset signal to the second sampler based on thesecond average value of the boundary data.
 2. The method according toclaim 1, further comprising: generating a data clock based on theboundary data; generating a boundary clock that is out of phase with thedata clock; sending the data clock to the first sampler; and sending theboundary clock to the second sampler.
 3. The method according to claim2, wherein the boundary clock is 180° out of phase with the data clock.4. The method according to claim 2, further comprising simultaneouslysending the data clock to the second sampler and the first sampler. 5.The method according to claim 1, determining whether the first averagevalue of the boundary data is greater than one-half; and in the eventthe first average value is greater than one-half, sending an offsetsignal to the second sampler indicating that the second sampler shouldbe compensated by a selected negative amount.
 6. The method according toclaim 1, determining whether the first average value of the boundarydata is less than one-half; and in the event the first average value isless than one-half, sending an offset signal to the second samplerindicating that the second sampler should be compensated by a selectedpositive amount.
 7. The method according to claim 1, further comprisingsending an offset signal to the first sampler based on the first averagevalue of the boundary data.
 8. The method according to claim 1, furthercomprising: setting the first data as boundary data; determining asecond average value of the boundary data over a selected period oftime; and sending an offset signal to the first sampler based on thesecond average value of the boundary data.
 9. The method according toclaim 8, further comprising generating a data clock based on theboundary data; generating a boundary clock that is out of phase with thedata clock; sending the data clock to the second sampler; and sendingthe boundary clock to the first sampler.
 10. The method according toclaim 8, further comprising sending an offset signal to the secondsampler based on the second average value of the boundary data.
 11. Themethod according to claim 1, further comprising: setting a first portionof the first data and a first portion of the second data as boundarydata; and after a period of time, setting a second portion of the firstdata and a second portion of the second data as boundary data.
 12. Themethod according to claim 1, wherein the boundary of the first datacomprises digital samples of a signal that carries the first data, asthe signal transitions between high and low values.
 13. A receivercomprising: a first sampler configured to sample a signal; a secondsampler configured to sample the signal; a clock and data recoverycircuit communicatively coupled with the first sampler and the secondsampler, the clock and data recovery circuit configured to: receivefirst data from the first sampler; receive second data from the secondsampler; offset logic communicatively coupled with the clock and datarecovery circuit, the first sampler and the second sampler, the offsetlogic configured to: determine a first average value from the boundaryof the first data over a selected period of time; send an offset signalto the first sampler based on the first average value; determine asecond average value from the boundary of the second data over aselected period of time; and send an offset signal to the second samplerbased on the second average value of the boundary data.
 14. The receiveraccording to claim 13, wherein: the clock and data recovery circuit isfurther configured to determine a clock adjustment signal based on theboundary data; and the receiver further comprises a clock generatorcommunicatively coupled with the clock and data recovery circuit, thefirst sampler, and the second sampler, the clock generator configuredto: generate a data clock based on the clock adjustment signal; generatea boundary clock that is out of phase with the data clock; send the dataclock to the first sampler; and send the boundary clock to the secondsampler.
 15. The receiver according to claim 13, wherein the offsetlogic is further configured to send an offset signal to the firstsampler based on the first average value of the boundary data.
 16. Thereceiver according to claim 13, wherein: the clock and data recoverycircuit is further configured to set the first data as boundary data;the clock generator is configured to send the data clock to the secondsampler, and send the boundary clock to the first sampler; and theoffset logic is configured to: determine a second average value of theboundary data over a selected period of time; and send an offset signalto the first sampler based on the second average value of the boundarydata.
 17. The receiver according to claim 16, wherein the offset logicis further configured to send an offset signal to the second samplerbased on the second average value of the boundary data.
 18. The receiveraccording to claim 13, wherein the clock generator is further configuredto: send the data clock to the first sampler; and simultaneously sendthe data clock to the second sampler.
 19. The receiver according toclaim 13, wherein the clock and data recovery circuit is furtherconfigured to set a first portion of the first data and a first portionof the second data as boundary data; and after a period of time, set asecond portion of the first data and a second portion of the second dataas boundary data.